The Productivity of C 3 and C 4 Plants: A Reassessment

Abstract

Plants with the C4 photosynthesis pathway have maximum rates of leaf photosynthesis (Pmax), under conditions of light saturation, that are about double those of plants with the C3 pathway (e.g. Gifford, 1974; Eagles & Wilson, 1982), though considerable variation exists between species within each group (Evans, 1975a; Pearcy & Ehleringer, 1984). These differences in Pmax were initially thought to give rise to greater biomass production in C4 plants, compared with C3 plants (e.g. Black, 1971; Zelitch, 1971; Marx, 1973), but doubts about such differences have since been expressed (e.g. Gifford, 1974; Evans, 1975a). The relative productivity of C3 and C4 plants is of considerable interest to both pure and applied ecologists. If the productivity of C4 species exceeds that of C3 species, it would be of considerable practical importance in crop production (e.g. Evans, 1975a), in pasture production (e.g. Leafe, 1988) and in energy production from biomass (e.g. Tieszen, 1983; Cannell, 1988). Conversely, if differences in rates of leaf photosynthesis between C3 and C4 species fail to give rise to differences in productivity, it would raise interesting questions for physiological ecologists. The main objectives of this paper are: 1 To draw attention to the inadequacies of previous comparisons of the biomass production of C3 and C4 species. 2 To examine a wider range of data and to consider more suitable ways of analysing the available data.